The prior art in railway right-of-way safety, with regards to hazards, has advanced little in decades. The prior art safety measures consist of Slide Detector Fences, Wash Out Detectors (WOD), monitoring electrical continuity through the rails, and direct observation of the railway right-of-way. Only the WOD have been recently developed. These decades-old safety measures continue to be installed.
A Slide Detector Fence (SDF) consists of a number of horizontal wires strung about 30 centimeters apart on a series of vertical wood poles typically spaced five to twenty meters apart. The poles are placed parallel to the railway track on the side that is susceptible to rockfalls. A rockfall or slide is detected by loss of electrical continuity when a single fragile wire is broken.
There are several problems with SDF. The wires can be broken by something as insignificant to safety as an animal or a tree branch. The SDF cannot discriminate between a small rock and a large boulder. The SDF must be repaired after each break or detection. Until repaired, all trains passing the SDF are required to pass the entire length of the SDF at a speed that will allow stopping within the range of vision, for example; short of a blockage or other hazard. This slowing of rail traffic causes a slowdown of opposing rail traffic in single track territory, backing up traffic in both directions. Sometimes additional relief train crews are required to complete the train's trip. Additionally, slowly traveling trains expend extra fuel to reaccelerate. Locating and repairing the break can be time consuming due to the remoteness of the areas where these fences are typically found, and the length of a single circuit of fence which can extend to upwards of one kilometer in length. SDF are not suitable for areas of slope near the natural angle of repose. In this type of region, there are boulders that may be loosened by a freeze-thaw cycle or rain; however, too many animals can break the SDF in such a region, so that the number of false alarms prohibits the use of SDF. SDF are primarily deployed between the tracks and near-vertical cliffs.
The WOD are installed to stop catastrophic accidents such as the Canadian National Rail (CN) accident at Conrad, B.C., Canada on Mar. 26, 1997. In that accident, two locomotives and eight rail cars derailed into a large depression that was created by a landslide. The two CN crew members on board the lead locomotive were killed. The diesel fuel caught fire and ignited another standing train's load of sulfur. More details are available in the Transport Safety Board of Canada (TSB) report No. R97V0063.
A WOD has two forms. The original form, installed on CN's main line, consists of a wire, fabricated from material similar to the SDF, with weights attached. The wire and weights assembly is buried beneath the right of way, in an area of suspect earth stability. Should the earth wash out or otherwise subside, the weights will break the wire causing a loss of electrical continuity which, in turn, activates a signal to warn approaching trains. There has never been a detection of subsidence on this system due to the very limited number of installations. An advance in WOD technology was made in late 1997. It involved the use of mercury tilt switches installed on posts inserted into the subgrade of the railway right-of-way. If the ground washes out or shifts to cause a change in attitude of the post, the mercury switch will tilt sufficiently to cause a loss of electrical continuity. Similarly, if the connecting wire is broken there will be a loss of electrical continuity. The loss of electrical continuity will trigger an alarm causing trackside signals to give a warning and a radio message to be broadcast to the trains nearby, informing their crew members that there is a suspected washout.
WOD are very limited in use. They are difficult to repair and expensive to install. During construction they disturb the track bed they are meant to protect. If they are installed too close to the surface, they may be disturbed by the normal subgrade movements caused by the trains. If installed too deeply, they may miss a small washout.
Another method of monitoring rail lines currently in use involves detecting a problem by sensing a loss of electrical continuity through the rail. A break may occur because of service stresses of trains and equipment, because of thermal contraction on the coldest of winter days, because the road bed subsides under the track, or because a rock strikes one of the rails with sufficient force. If either of the rails break, the loss of electrical continuity changes the block, interlocking or Centralized Traffic Control (CTC) trackside signals to their most restrictive indication. These signals are similar to an intersection traffic light. The signals do not, by themselves, stop any train; they must be acted on by the train crew, who must witness such a signal prior to rolling over the location of the break. Crews whose train has already traveled past the last one of these signals when a break occurs in the train's present block receive no indication of a broken rail.
The electrical continuity of the track can remain even if there is a sizable chasm created by a washout beneath the track. The Conrad accident had a chasm of about 70 meters of unsupported track that did not break until a train came upon it. Similarly, on Sep. 22, 1993, a barge, being shoved in dense fog, struck a span over Big Bayou Canot in Alabama USA. The bridge was knocked several feet out of alignment. Eight minutes later an Amtrak train derailed off the bridge at 116 km/h. (72 m.p.h.), killing 47 people. The rails, although bent and unable to support and guide a train, continued to be electrically continuous and therefore did not give any warning through the trackside signal system. More details are available in National Transportation Safety Board report adopted Sep. 19, 1994, Notation 6167B. In addition, rocks as large as automobiles can fall onto the track without breaking the sturdy rails.
The SDF, the original WOD, and the rail electrical continuity detection systems all depend on receiving a detection before the train crew observes the last signal on approach to the hazard. In many areas, the trackside signals are several kilometers apart. Thus, there is time for a hazard to occur without the crew receiving information through the trackside signal system.
Another method of track hazard detection depends on observation. A hazard may be seen by a member of the train crew during their tour of duty, during routine or random Track Patrols, or while investigating reports from the public.
Many of the areas that rockfalls and washouts occur are remote and are not frequented by the public. As well, these rights-of-way are private property and most railway companies discourage the public's presence. The trains run 24 hours a day. The public would be unlikely to see hazards except by daylight. The natural hazards that cause these accidents are most frequently caused by severe weather such as higher than normal rainfall. This weather is frequently accompanied by diminished visibility. These two conditions make the public less likely to be present or to observe hazards in remote areas. People traveling the roadways that parallel the tracks offer a good chance of spotting a dangerous situation. Even if a dangerous condition was sighted, the public may not be inclined or able to report it. These typically remote areas are not normally served by cellular phone companies and the railway's phone number may be difficult to obtain. Relying on the public to report hazards is simply not a dependable solution.
Routine or random track patrols can spot a hazard that has occurred. They can give, if conscientious enough, some insight into the possibility of emerging dangerous areas some of the time. In many cases, however, a hazard such as a rockfall occurs suddenly. The history of the area would indicate, with more accuracy, the likelihood of rockfalls. This is the type of area where SDF are installed. The two drawbacks of the patrols are the cost involved in manual observation and, in CTC, the delay to trains. A track patrol is typically a highway-rail vehicle; a pickup truck with an extra set of wheels attached that fit the rails, but of much smaller diameter and weight than standard rolling stock wheels. Rolling stock includes locomotives and standard rail cars, also referred to as `equipment` in the Canadian Rail Operating Rules (CROR). A hydraulic system to raise and lower the extra set of wheels is provided. The patrols are used to precede a train along the track. The small diameter of wheels and need to stop short of a hazard may not permit the highway-rail vehicle to travel at speed over 40 km/h. Thus on 60 km/h (35 miles per hour) track, the patrol must wait for trains to pass, then get on the track, patrol, then get clear of the track and report to the Rail Traffic Control (RTC) staff typically 15 minutes minimum prior to the expected arrival of the next train. To be any closer than 15 minutes or 10 kilometers would not allow the following train to continue at full track speed because of the workings of the CTC signal system. Consequently, even if every train could be preceded by a patrol, conditions may change in the 15 minute period required between the safety inspection vehicle and the train. At present, CN has five patrols in about 200 kilometers (125 miles) of high risk track.
Generally, when a train is the first to encounter a hazard on the track, it cannot stop short of the hazard. Trains take a long distance to stop. Stopping distance is a function of, amongst other things: speed, track grade, brake set up, total weight of the train, steel-on-steel friction, and the length of the train. Steel-on-steel friction is, in most cases, less than half of that of rubber-on-pavement experienced by cars. Train length is significant because the air brake application can only propagate through the train at the rate of the speed of sound through the train's air brake pipe. The air brake pipe is built into all equipment with connecting hoses at each end of the equipment. This allows for control of the brakes on a series of rail cars from a locomotive, when the hoses are joined. This continuous air brake pipe propagates the changing air pressure required to actuate the brakes. It will take about 6 seconds for a change in pressure to propagate through an 1800 meter long (6000 foot) train. In other cases there may be little opportunity to see the hazard because of darkness, curved track, or snowfall. One hazard that is not easily seen is a change in the gauge of the track, sometimes caused by a rolling rock striking a rail. Gauge is the standard distance between the inside of the pair of rails.
Several types of remote-controlled companion or pilot railway cars have been proposed. They explore the track in front of the locomotive or train at a distance that allows the train to stop if a dangerous condition is detected. Examples of such systems can be found in U.S. Pat. Nos. 5,627,508 and 5,623,244 to Cooper et al. (1997), and U.S. Pat. No. 5,429,329 to Wallace et al. (1995). These inventions have not enjoyed commercial success because they require modifications to the CTC signal system. Furthermore, they are expensive to build and maintain and they occupy track that could be used for revenue generating rolling stock, most noticeably when train and companion car are in a siding. Less noticeably, but more significantly, these inventions would cause a greater spacing of trains proceeding in either direction, much like the track patrols. These pilot vehicles do not detect a dangerous event that occurs between the time at which it inspects the track and the time at which the train arrives. If notice could be given to the train crew, an emergency train brake application may reduce the negative consequences. For example, a rock slide may derail less rail cars if advance notice was given. However, as yet, no pilot vehicle communicates with the RTC office.
One prior art system, U.S. Pat. No. 5,713,540 (1998) to Gerszberg et al, uses detected sound to indicate railway activity. The Gerszberg system monitors the rails in pairs and identifies a dangerous condition by noting the difference in detections between the rails. If a rock struck the track it would be heard louder on one rail when compared to the other rail. Also, the Gerszberg system generates an alarm when there is a very large sound detected on both rails. Such a system however, is unable to distinguish between a small event occurring near an acoustic sensor from a large event occurring at a distance. Also, some tracks have metal bars or concrete ties that tie the rails together. These may act as sound conductors and eliminate or substantially reduce the measurable difference between the sounds on each rail making it significantly less likely to detect the anticipated difference in sounds. The Gerszberg system has no locating feature. The physical event that was acoustically sensed cannot be located with any accuracy. It employs only microphones and has a lower limit of sound detection of 30 hertz. Rockfalls may be more easily detected by sensing vibrations of much lower frequencies. It has a digital signal processor to provide audio signature analysis but has no attenuation calculation to ascertain the original acoustic energy of the physical event. The Gerszberg system cannot be used near a public crossing or the initial filtered signals will require a higher threshold before generating an alarm. Comparing the pairs of detections between rails might generate a false alarm in cases of thermal expansion and accompanying rail creep. It has no feature that would stop an endangered train without the locomotive driver's actions. Lastly, the Gerszberg system cannot detect mud slides, snow and rock avalanches, and other low acoustic energy events that may be hazardous.
Before the 1980's, the conventional method of stopping a train was by opening an anglecock on the brake pipe and releasing some or all of the pressurized air. That was done from the locomotive, for controlled stops, or from the caboose for emergency stops. The locomotives are equipped with a special slow-reduction valve. During the 1980's, the art of remote train braking advanced somewhat with the development of an end of train device or the Sensing and Braking Unit (SBU). The SBU is a wireless transmitting and receiving box that is secured to the last car of a train, and replaces some functions of a caboose. The SBU is attached to the air brake pipe. One function of the SBU is to initiate an emergency brake application on the train when it receives a wireless communication signal. This gave the locomotive engineer the capacity to stop the train from the locomotive in emergency situations via an SBU attached to the last car. Should there be a pinched air hose or otherwise blocked brake pipe, the train could still be stopped. This system was meant for the exclusive use of the crew of that train only.
An object of the present invention is to provide an early warning system for trains which has the following advantages:
(a) continuous monitoring of the track even after a train passes the last signal on approach to a hazard; PA1 (b) instant RTC, crew and train notification of a hazard so the train can be stopped at any time; PA1 (c) low operational costs, namely the price of electricity to operate sound recognition and alarm equipment; PA1 (d) low maintenance costs with no need for repairs after a detection of a fallen rock; PA1 (e) post hazard notification allowing trains to resume normal track speed after the first train has passed the location of the suspected hazard, PA1 (f) a method of deducing the exact location of the suspected hazard, so a train need only be restricting its speed on approach to that location; PA1 (g) an alarm system where the train need not slow down if a track patrol can inspect the potential hazard prior to the train's arrival; PA1 (h) accurate and automatic compilation of the location, time and type of event that caused the alarms; PA1 (i) an ability to deduce the size and therefore the danger of a rockfall or physical event; PA1 (j) an ability to sense vibration from physical events below 30 hertz; PA1 (k) minimal use of fossil fuels and therefore environmentally friendly.
Further objects and advantages will become apparent from considering the ensuing description.